1. Field of the Invention
The present invention relates to a moving amount detecting method widely used in various kinds of encoders, etc.
2. Description of the Related Art
The moving amount of a detected body is detected by irradiating light from a light source to the detected body and detecting light reflected from the detected body or light transmitted therethrough using a photodetector. Such detection is widely performed and constitutes one kind of optical instrumentations.
The inventors of this application proposed a method for detecting a displacement amount, etc. of the detected body in Japanese Patent Application No. 63-127916. In this method, a light beam from a light source emitting coherent light is irradiated onto the detected body having a periodic structure so as to form a shadow picture pattern by diffraction. The displacement amount of the detected body is detected by using this shadow picture pattern.
However, in this method, the light source is limited to a source from which the coherent light is emitted. Therefore, the cost of a measuring device tends to be increased.
There is another known method for detecting a moving amount, etc. of the detected body by irradiating an incoherent light beam emitted from an LED onto the detected body having a monoperiodic structure. Such a method is described in e.g., "Sensor-Interfacing" (S61) No. 3, P. 29 published by CQ publishing company. In this method, when a pitch of the monoperiodic structure of the detected body is reduced to improved the accuracy in measurement, an S/N ratio of a signal obtained by the photodetector is greatly reduced so that it is difficult to measure the moving amount, etc. of the detected body with high accuracy.